This invention relates generally to composite constructions comprising a hard material phase and a relatively softer ductile material phase and, more particularly, to composite constructions having an ordered microstructure of polycrystalline diamond and a relatively softer ductile material to provide improved mechanical and/or thermal properties, when compared to traditional constructions formed from polycrystalline diamond alone.
Polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN) constructions, synthesized by high temperature/high pressure processes, are well known for their mechanical properties of hardness and wear resistance, making them a popular material choice for use in such industrial applications as cutting tools for machining, mining and drilling where such mechanical properties are highly desired. For example, PCD and PCBN constructions are provided in the form of surface coatings on, e.g., inserts used with cutting and drilling tools to impart properties of hardness and wear resistance thereto.
Traditionally, such PCD and PCBN inserts are formed by coating a carbide substrate with one or two layers of PCD or PCBN. Such inserts comprise a substrate, a surface layer, and often a transition layer to improve the bonding between the exposed layer and the support layer. The substrate is, most preferably, a carbide substrate, e.g., cemented carbide, tungsten carbide (WC) cemented with cobalt (WCxe2x80x94Co). The coated layer or layers of PCD conventionally comprises a metal content from 10% to 30% by weight to facilitate intercrystallline bonding and bonding of the layers to each other and to the underlying substrate. Metals employed are often selected from cobalt, iron, or nickel and/or mixtures or alloys thereof and can include metals such as manganese, tantalum, chromium and/or mixtures or alloys thereof. However, while higher metal content typically increases toughness, higher metal content also decreases hardness, thereby limiting the flexibility of providing coatings with the requisite properties. Additionally, when variables are selected to increase hardness, typically brittleness also increases, thereby reducing the toughness of the cutting element.
Generally, PCD and PCBN each exhibit extremely high hardness and provide a high degree of wear protection to a cutting element. However, in more complex wear environments causing impact and fretting fatigue, layers comprising PCD and PCBN may fail by gross chipping and spalling. For example, inserts coated with a thick PCD monolayer may exhibit brittleness that causes substantial problems in practical applications. Conventional methods of improving the performance of PCD or PCBN layers include controlling particle size to maximize toughness, but the effect is limited.
It is, therefore, desired that PCD and PCBN composite constructions be provided that are specifically designed to have improved properties of fracture toughness, when compared to conventional PCD and PCBN constructions, hereby reducing the potential for conventional PCD and PCBN failure modes of spalling and/or chipping. It is desirable that PCD and PCBN composite constructions have such improved fracture toughness without sacrificing other desirable properties of wear resistance and hardness associated with the PCD and PCBN materials. It is desired that such composite constructions be adapted for use in such applications as cutting tools, roller cone bits, hammer bits, drag bits and other mining, construction and machine applications where properties of improved fracture toughness is desired.
Composite constructions of this invention generally comprise an ordered microstructure of multiple structural units that each comprise at least a first structural phase and a second structural phase that are intentionally arranged and formed from materials that are selected to provide improved properties of fracture toughness when compared to traditional materials formed from PCD or PCBN alone.
A structural unit first structural phase comprises a hard material that is selected from the group consisting of cermet materials, PCD, PCBN and mixtures thereof. A structural unit second structural phase comprises a material that is different than that selected to form the first structural phase, e.g., one that is relatively softer and/or more ductile that the material selected for the first structural phase. Additionally, the second structural phase is in contact with at least a portion of the first structural phase.
Composite constructions of this invention having order microstructures may also take the form of multi-layer structures. Such multi-layer constructions comprise two or more layers, e.g., a first layer and at least a second layer disposed onto a surface of the first layer. In such multi-layer embodiment, at least one of the layers comprises a composite construction having an ordered microstructure made up of the multiple structural units that are formed from the materials as described above.
Composite constructions of this invention provide improved properties of fracture toughness, when compared to conventional non-composite materials comprising PCD or PCBN alone, without substantially sacrificing other desired properties of wear resistance and hardness, thereby reducing the potential for material failure by spalling and/or chipping.